Production of activated char using hot gas

ABSTRACT

A gas mixture preheated to high temperatures using an oxy-fuel, an oxygen-enriched air-fuel or an air-fuel burner is used to devolatilize and partially oxidize carbonaceous feedstock, thereby producing an active residual char that can be used in applications utilizing activated carbon. Use of hot gas and ground carbonaceous feedstock allows the equipment to be minimized, thereby allowing the activated carbon to be produced at or near points of use, for example the production of activated char at or near utility boilers for use in the reduction of mercury emissions from flue gas streams.

TECHNICAL FIELD

The present invention relates generally to methods and systems toproduce activated char such that production can occur at or near the enduse point.

BACKGROUND OF THE INVENTION

Activated carbon is a widely used adsorbent in industrial processes toremove contaminants from gas or liquid streams. For example, attempts tomeet currently pending mercury emissions limits for fossil fuel firedpower plants by injecting powdered activated carbon (PAC) into the fluegas upstream of a particulate control device in order to removecontaminants from the flue gas are being investigated.

The removal of mercury from flue gas streams from combustion processesis of significant interest. The toxicity of mercury to humans has longbeen known. An example of the devastating effects of mercury exposureoccurred in Minamata, Japan in the 1950's where organic mercurybyproducts of acetaldehyde production were discharged into the localbay, and were ingested and metabolized by fish. By consuming fish in thebay, wide spread neurological damage and birth defects to the localpopulation were reported.

Coals used for various combustion processes typically contain about 0.1ppm mercury. In the United States alone, about 50 tons of mercury aredischarged as vapor in stack gas every year. Through chemical andbiological processes, such mercury can become concentrated by manythousand-fold into fish, thus entering human food supplies at harmfullevels. In December 2000, the Environmental Protection Agency (EPA) madeits regulatory decision that mercury emissions from coal-fired electricgenerating plants need to be controlled.

One barrier to the use of adsorbents, however, has been the high cost ofboth producing and shipping PAC to the end use point. PAC is typicallyproduced from carbonaceous starting materials such as coal, wood,biomass materials, nutshells (e.g., walnut shells, palm nut) or nuthulls (e.g., coconut) that initially do not have high adsorptivecharacteristics. The carbonaceous starting materials are converted intoPAC materials exhibiting higher adsorptive properties by energy andcapital intensive processes that include pyrolyzing the feedstock in arotary kiln, activating the carbon with an activation media (i.e.steam), and grinding or pulverizing the resulting char. The activatedcarbon material must then be shipped to its end use point, such as acoal-fired power plant.

Attempts to produce PAC near an end use point have been made. Forinstance, the use of a combustion process to produce char for mercurycontrol has been discussed in the patent literature. U.S. Pat. No.6,451,094 B1 to Chang, et al. discuss injecting a feedstock into a hotflue gas and activating the feedstock in situ.

U.S. Pat. No. 6,595,147 to Teller et al. relates to adding acarbonaceous char to the flue gas while it is still within a resourcerecovery unit at a temperature high enough to devolatilize the materialto form activated char in situ.

Attempts have also been made to use carbon found in fly ash to capturemercury from flue gas in coal-fired processes. U.S. Pat. No. 5,787,823to Knowles proposes a method in which carbon-containing fly ash iscaptured in a cyclone upstream of a conventional particulate controldevice (PCD). The captured material is then injected into a duct tocapture mercury. U.S. Pat. No. 6,027,551 to Hwang, et al. teachseparation of the carbon from fly ash captured in a conventional PCD andinjection of the carbon-rich portion as a mercury sorbent.

U.S. Pat. No. 6,521,021 B1 to Pennline et al. teach removing partiallyoxidized coal from the combustion zone of a boiler. The coal isseparated out and injected further downstream as a mercury sorbent.

Lanier, et al. (U.S. Pat. No. 6,726,888 B2) suggest controlling thecombustion process such that both the NOx emissions and thecharacteristics of the native fly ash for mercury removal arecontrolled.

Given both the constraints of normal boiler operation, and the fact thatthe activity of the native residual carbon decreases as it moves throughthe boiler, separate production processes for activated carbon canprovide a better opportunity to produce activated carbon havingcharacteristics favorable for an intended and particular end use. Itwould therefore be desirable to provide systems and methods for onsiteproduction of activated carbon suitable for a wide range of processes,thereby improving the cost and efficiency of activated carbon productionuse.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods and systems for production ofactivated char that are sufficiently flexible and efficient such thatproduction can occur near or at the end use site of the activated char.The methods and systems provided herein can also be used in otherarrangements. For example, the present invention can be implemented fora central facility to produce activated char as described herein and toserve multiple utilities or the like. In another implementation, thepresent invention can be used by a utility to make activated char forits own plant and ship excess activated char to other locations.

Such methods and systems include preheating a gas mixture to hightemperatures using an oxy-fuel, an oxygen-enriched air-fuel or anair-fuel burner to form a hot gas stream. The hot gas stream is mixedand reacted with a carbonaceous feedstock (i.e. carbonaceous rawmaterial) in a manner such that the carbonaceous feedstock isdevolatilized and partially combusted to thereby produce an activeresidual char that can be implemented in a variety of applications thatuse activated carbon.

Use of hot gas and ground carbonaceous feedstock allow the equipment tobe minimized, thus allowing the activated carbon to be produced at ornear the point of use, for example to reduce utility boiler mercuryemissions from flue gas.

The present invention includes a method to produce activated char at ornear the end use point. A hot (preferably about 2000-3000° F.) oxidizinggas stream mixes and reacts with a ground or pulverized carbonaceousfeedstock to create powdered activated char with adsorbent propertiessimilar to powdered activated carbon produced with the same carbonaceousfeedstock. Alternatively, an inert gas could be heated and used topyrolize the feedstock. It will be appreciated by those skilled in theart that such adsorptive properties are dependent on the feedstockutilized. It will also appreciated by those skilled in the art thatwhile adsorptive properties of an activated char may be sufficient forsome applications, the activated char may need to be altered for otherapplications.

The present invention thus provides several benefits including, but notlimited to, the ability to produce activated char at or near the end usepoint, lower cost and more efficient production methods for activatedchar relative to large, rotary kiln methods and an option to use acarbonaceous feedstock for producing activated char that may bedifferent from the fuel used in the main combustion process of a givenfacility. Consequently, the present invention provides the flexibilityto alter activated char properties for a specific application at or nearthe end use point.

The surface area of the activated char produced in accordance with thepresent invention may be less than, and in some cases significantly lessthan, the surface area of currently and commercially available PACs.Given the efficient and flexible methods provided herein, however, theoverall economics may still favor use of activated char produced inaccordance with the present invention, even in situations where moreactivated char may be necessary relative to currently and commerciallyavailable PACs.

The hot gas stream, which can include steam, oxygen, or mixtures ofgasses, is produced by preheating a gas stream with an oxy-fuel, anoxygen-enriched air-fuel or an air-fuel burner to create a hot andhighly reactive gas mixture. The high turbulence from the hot-gas servesto rapidly mix the carbonaceous feedstock with the hot-gas. In apreferred embodiment of the invention, the elevated temperature and theoxygen concentration of the hot gas cause rapid ignition,devolatilization and partial oxidation of the carbonaceous feedstock.

Because both elevated temperature and high oxygen concentrations havebeen shown to significantly increase the devolatilization rate ofcarbonaceous fuels, the use of hot oxidizing gas reduces the residencetime required to produce the activated carbon material. Consequently,small reactors can be used to replace the large rotary kilns typicallyused to produce activated carbon. In addition, by-products (such as COand H₂) produced in accordance with this process can be used either asfuel for the main boiler or as a reburning fuel.

The present invention provides methods and systems for separatingactivated char production from the main combustion process, therebymaking it possible to produce activated char having properties (e.g.,adsorptive) desirable for a specific application. For example and whilenot to be construed as limiting, the present invention enables theonsite (or near end use) production of activated char for a pulverizedfuel-fired utility for the removal of mercury in a flue gas stream.Alternatively or in addition, the present invention enables theproduction of activated char to be tailored for use in a fixed bedarrangement for waste water treatment to remove hydrocarbons and othercontaminants. Another advantage of the present invention is the abilityto use the partial oxidation gas as a useful fuel in the process, eitherby recirculating this material to the hot gas burner or by firing itinto a boiler that may, or may not, be part of the process. For example,the gas products could be sent to the boiler as a reburning fuel for NOxcontrol.

As discussed above, the hot oxygen or hot gas burner as used inaccordance with the present invention allows for on-site activated charproduction. The combination of high temperatures and good mixingachieved with this burner allows activated char production withrelatively small, simple process equipment (especially as compared tothe rotary kilns currently used to produce PAC). Moreover, activation ofthe activated char of the present invention occurs as a result of theprocess as opposed to rotary kiln methods which typically requireseparate activation steps.

Accordingly, the present invention can significantly reduce the cost ofactivated char for the end user by both improving the productionefficiency and versatility as well as minimizing shipping requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference should be made to the following DetailedDescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates a schematic view of apparatus to produce activatedcarbon in accordance with one embodiment of the present invention;

FIG. 2 illustrates a schematic view of apparatus to produce activatedcarbon in accordance with an alternative embodiment of the invention;and

FIG. 3 illustrates a schematic view of apparatus to produce activatedcarbon in accordance with yet another alternative embodiment of theinvention.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION

The present invention provides methods and systems for production ofactivated char near or at the end use point of the activated char. Suchmethods and systems include preheating a gas mixture to hightemperatures using an oxy-fuel, an oxygen-enriched air-fuel or anair-fuel burner to form a hot gas stream. The hot gas stream is mixedand reacted with a carbonaceous feedstock (i.e. carbonaceous rawmaterial) in a manner such that the carbonaceous feedstock isdevolatilized and partially combusted to thereby produce an activeresidual char that can be implemented in applications that use activatedcarbon.

Use of hot gas and ground carbonaceous feedstock allow the equipment tobe minimized, thus allowing the activated carbon to be produced at ornear the point of use, for example to reduce utility boiler mercuryemissions from flue gas.

The present invention includes a method to produce activated char at ornear the end use point. A hot (preferably, 2000-3000° F.) oxidizing gasstream mixes and reacts with a ground or pulverized carbonaceousfeedstock to create powdered activated char with adsorbent propertiessimilar to activated char produced with the same carbonaceous feedstockfrom typical methods such as rotary kiln processes. It will beappreciated by those skilled in the art that such adsorptive propertiesare dependent on the feedstock utilized. It will also be appreciated bythose skilled in the art that while adsorptive properties of anactivated char may be sufficient for some applications, the activatedchar may need to be altered for other applications.

The present invention thus provides several benefits including, but notlimited to, the ability to produce activated char at or near the end usepoint, lower cost and more efficient production methods for activatedchar relative to large, rotary kiln methods and an option to use acarbonaceous feedstock for producing activated char that may bedifferent from the coal used in the main combustion process of a givenfacility. Consequently, the present invention provides the flexibilityto alter activated char properties for a specific application at or nearthe end use point.

The hot gas stream, which can include steam, oxygen, or mixtures ofgasses, is produced by preheating a gas stream with an oxy-fuel, anoxygen-enriched air-fuel or an air-fuel burner to create a hot andhighly reactive gas mixture. The gas mixture is then rapidly mixed withthe carbonaceous feedstock. In a preferred embodiment of the invention,the elevated temperature and the oxygen concentration of the hot gascause rapid ignition, devolatilization and partial oxidation of thecarbonaceous feedstock.

Because both elevated temperature and high oxygen concentrations havebeen shown to significantly increase the devolatilization rate ofcarbonaceous fuels, the use of hot oxidizing gas reduces the residencetime required to produce the activated carbon material. Consequently,small reactors can be used to replace the large rotary kilns typicallyused to produce activated carbon. In addition, by-products (such as COand H₂) produced in accordance with this process can be used either asfuel for the main boiler or as a reburning fuel.

The present invention thus provides methods and systems for separatingactivated char production from the main combustion process, therebymaking it possible to produce activated char having properties (e.g.,adsorptive) desirable for a specific application. For example and whilenot to be construed as limiting, the present invention enables theproduction of activated char for a pulverized fuel-fired utility for theremoval of mercury in a flue gas stream. Alternatively or in addition,the present invention enables the production of activated char to betailored for use in a fixed bed arrangement for waste water treatment toremove hydrocarbons, water and other contaminants. Another advantage ofthe present invention is the ability to use the partial oxidation gas asa useful fuel in the process, either by recirculating this material tothe hot gas burner or by firing it into a boiler that may, or may not,be part of the process. For example, the gas products could be sent tothe boiler as a reburning fuel for NO_(x) control.

As discussed above, the hot oxygen or hot gas burner as used inaccordance with the present invention allows for on-site activated charproduction. The combination of high temperatures and good mixingachieved with this burner allows activated char production with verysmall, relatively simple process equipment (especially as compared tothe rotary kilns currently used to produce PAC). Moreover, activation ofthe activated char of the present invention occurs as a result of theprocess as opposed to rotary kiln methods which typically requireseparate activation steps.

Accordingly, the present invention can significantly reduce the cost ofactivated carbon for the end user by both improving the productionefficiency and versatility as well as minimizing shipping requirements.

As previously discussed, the present invention can be used to produceactivated char suitable for a wide range of industrial processes. Theoptimal configuration for production of activated char for a particularapplication therefore depends strongly on the end use and the desiredchar characteristics. For purposes of illustration, ratios of hot gas tocarbonaceous feedstock, residence time, temperature of the hot gas andadditives to the process can be determined based on the intended end useof the activated char and economic factors.

Referring now to FIG. 1, a schematic view of apparatus to produceactivated carbon in accordance with one embodiment of the presentinvention is shown.

Burner 1 can be used in a variety of modes, with the burner design beingaltered as necessary to account for the mode of operation. In onepreferred embodiment, burner 1 is an oxy-fuel burner and operates onfuel 10 and oxidant source 11 to produce a very hot flue gas. In thisembodiment, oxidant 11 is pure oxygen. In another embodiment, burner 1is used in an oxygen-enriched mode of operation. More specifically,oxidant 11 has an oxygen concentration less than pure oxygen, butgreater than air (e.g, an oxygen concentration of between about 21 andless than 100%). This embodiment may not be as preferred because of thepresence of nitrogen in the air. The N₂ in the hot gas can act as adiluent for the reaction with the carbonaceous feedstock and lowers thetemperature of the hot gas. In yet another embodiment, burner 1 isoperated as an air burner. Oxidant 11 in this embodiment is air. Thisthird embodiment may also be not as preferred as the oxy-fuel modebecause of the presence of N₂ in the air. The presence of N₂ in the hotgas can act as a diluent for the reaction with the carbonaceousfeedstock and lowers the temperature of the hot gas.

Fuel 10 and oxidant 11 are fed to hot oxygen burner 1. Exemplary fuelsfor fuel 10 include, but are not limited to, natural gas (NG), methane,propane, hydrogen, light oil, LPG, fuel oil and coke oven gas. Fuel 10can be liquid, but is preferably a gas.

In some embodiments, it may be preferred to introduce reactant gas 12into burner 1 where it is mixed and reacted with oxidant 11 and fuel 10.Reactant gas 12, which can be steam, can be used primarily to obtain adesirable composition for gas stream 7 for proper reaction withcarbonaceous feedstock in reaction vessel 3. Reactant gas 12 is alsoused to modify the properties of the activated char produced in reactionvessel 3. For example, reactant gas 12 can be used to enhance thesurface area of the resulting char produced in reaction chamber 3. Itwill be appreciated that reactant gas 12 may not always be necessary.

In particular embodiments where burner 1 is used in the oxy-fuel oroxygen-enriched air-fuel modes, burner 1 can be configured as a hotoxygen burner such as those disclosed in U.S. Pat. No. 5,266,024 toAnderson, the entire contents of which are incorporated herein byreference. These hot oxygen burners can produce a high velocity, hot andhighly reactive gas mixture known as “hot oxygen”.

Regardless of whether burner 1 is operated in an oxy-fuel,oxygen-enriched or air mode of operation, it is necessary to have asufficient amount of oxygen in gas stream 7 to burn and partiallyoxidize carbonaceous feedstock 13 to thereby generate activated charhaving adsorptive properties for its intended end use. The oxidationpotential of gas stream 7 is such that carbonaceous feedstock 13 will bepartially oxidized and will not be completely consumed in order togenerate the desired activated char. The amount of oxygen in gas stream7 is accordingly adjusted based on the amount of desired reaction offeedstock 13. In order to generate the proper amount of oxygen in gasstream 7, the amount of oxidant 11 and/or fuel 10 can then be adjusted.It is important that too much oxygen not be used in order to avoid toomuch consumption of feedstock 13, which would result in poor productyield.

If excess oxygen relative to fuel 10 is desirable in stream 7 (forexample to enhance the reaction with carbonaceous feedstock 13 when noother streams such as steam are being used), the stochiometric ratio ofoxidant 11 fed to burner 1 will be in vast excess for fuel 10. In othermodes of operation, burner 1 will be operated between nearstoichiometric and in vast oxygen excess of oxidant 11 to fuel 10.

Hot oxygen burner 1 produces a high temperature gas stream 7, preferablyhaving a temperature equal to or greater than 800° F. and mostpreferably greater than 2000° F. The temperature of hot gas stream 7 issufficiently high to cause the desired reaction with feedstock 13 (andany carrying material for feedstock 13). Gas stream 7 will primarilycontain products of combustion (e.g., CO₂ and H₂O), residual oxygen, anyunreacted gas from gas stream 12 and possibly N₂ if air is used as partof or all of oxidant 11. In some embodiments, gas stream 7 may containgreater than 70% by volume residual oxygen with the balance beingproducts of combustion.

As further illustrated in FIG. 1, ground or pulverized carbonaceousfeedstock 13 is fed to mixing section 2 and mixed with hot gas mixture7. Carbonaceous feedstock 13 can be selected from a variety ofcarbonaceous raw materials such as a variety of coals, petroleum coke,biomass materials (e.g., saw dust) or nutshells (e.g., walnut shells,palm nut) or nut hulls (e.g., coconut). Carbonaceous feedstock 13 can beconveyed to mixing section 2 by a variety of methods.

Carbonaceous feedstock 13 may be conveyed to mixing section 2 byentrainment in a carrier gas such as air or flue gas, pneumaticallysupplied, in a slurry such as a water slurry. It will be appreciated bythose skilled in the art that other methods of conveying feedstock 13may also be employed, including supplying the feedstock by itself,without a carrying or conveying material. Any oxygen in the conveyingstream should be accounted for in the overall ratio of oxygen tofeedstock (i.e., oxygen in the conveying stream combines with the oxygenin stream 7).

The velocity of gas stream 7 produced from burner 1 and fed to mixingsection 2 is sufficiently fast such that carbonaceous feedstock 13together with any conveying material, regardless of how feedstock 13 issupplied (e.g. entrained in a carrier gas, pneumatically supplied, as aslurry) to mixer 2, will be entrained in gas stream 7.

Those skilled in the art will appreciate that carbonaceous feedstock 13can be selected based on a variety of criteria, including the end use ofthe activated carbon produced in accordance with the present invention.For example, it may be desirable to use a particular pulverized coal forapplications using activated carbon in a dispersed phase capture mode(e.g. capture of mercury in a flue gas stream). In contrast, it may bepreferred to use a crushed coal in applications where the activatedcarbon is to be used in packed beds (e.g., fixed bed arrangement forwaste water treatment to remove hydrocarbons and other contaminants fromgas or liquid streams).

It will likewise be appreciated by those skilled in the art that theresidence time in reaction vessel 3 (discussed herein) will be affectedby the selection of feedstock 13. For example, the residence time forpulverized feedstocks for dispersed phase modes of adsorption may be onthe order of seconds as compared to residence times for crushedfeedstocks, which may be on the order of minutes. Carbonaceous feedstock13 is thus ground or pulverized to a desirable size depending on the enduse and the equipment design.

In some embodiments, it may be desirable to pretreat carbonaceousfeedstock 13 with a dopant. For example, carbonaceous feedstock 13 canbe pretreated with a halide salt (e.g., KBr) such that the halide saltis dispersed in carbonaceous feedstock 13 prior to being introduced intomixing section 2. This may be beneficial in applications where theactivated carbon will be used for mercury capture and removal from fluegas streams. The halide salt (e.g., KBr) can improve the activated charcharacteristics in this type of application. Preferred examples of suchtreatment can be found in commonly owned U.S. patent application Ser.No. ______ entitled “Catalytic Adsorbents For Mercury Removal From FlueGas and Methods of Manufacture Therefor” to Chien-Chung Chao et al.,filed on even date herewith, the entire contents of which are herebyincorporated by reference.

Combined stream 8 thus contains a mixture of feedstock 13 and hotreactant gas 7. Stream 8 is introduced into reactor vessel 3. Reactorvessel 3 may be a refractory lined pipe with water cooling as needed.Alternatively, water sprays could be used to control the temperature inthe reactor.

As also shown in FIG. 1, other additive fluids, solids or gases 14 b maybe added into reaction vessel 3. Exemplary additive 14 b may include,but is not limited to, steam, N₂, water and/or material(s) that have aspecific activity for an intended use of the activated char. Forinstance, stream 14 b may be used to adjust the temperature withinreactor 3 and/or provide steam for the reaction within reactor 3. In thealternative or in addition to additive 14 b, additive fluid, gas orsolid (e.g., lime) 14 a may also be mixed with stream 8 prior toinjection into reaction vessel 3.

As previously discussed, the materials in reaction vessel 3 undergodevolatilization and partial oxidation, resulting in a product streamcontaining partial oxidation gasses (e.g., CO and H₂) and activatedchar. The partial oxidation gases and activated char exit reactor vessel3 as stream 9.

Those skilled in the art will appreciate that the residence time, ratioof residual oxygen in gas stream 7 to carbonaceous feedstock, andreaction vessel 3 temperature are controlled based on carbonaceousfeedstock 13 and desired characteristics of the activated char. Forexample, if the residence time is too long, or the ratio of hot oxygento feedstock is too high, too much of the feedstock will be consumed.This can result in reduced product (i.e. activated char) yields. If theresidence time or reaction temperatures are too low, thedevolatilization and activation may be incomplete, thereby reducingproduct (i.e. activated char) quality.

Partial oxidation gases and activated char mixture 9 exiting reactionvessel 3 are quenched with a quenching media 15 to cool the products. Insome embodiments, it may be desirable to include additives (such as ahalide salt (e.g, KBr) for use of the activated char in removal ofmercury from flue gas streams) in quench media 15 which are mixed withthe activated char. Preferred examples of such treatment can be found incommonly owned U.S. patent application Ser. No. ______, entitled“Catalytic Adsorbents For Mercury Removal From Flue Gas and Methods ofManufacture Therefor” to Chien-Chung Chao et al., filed on even dateherewith, the entire contents of which are hereby incorporated byreference. The quenching media could be a fog of water dropletscontaining the desired additive, or a gas such as nitrogen.

Cooled mixture 21 may then be separated in a cyclone (or otherparticulate collection device) 4. Cyclone 4 may not always be necessary,for example in direct injection modes of use (see for example, FIG. 3).

A portion or all of partial oxidation gas 16 (e.g., carbon monoxide andhydrogen) exiting cyclone 4 can then be fed to boiler 5 as a reburningfuel 18 a, or returned to the combustion zone of the boiler as fuel 18b. Alternatively or in addition to using partial oxidation gas 16 asreburning fuel 18 a and/or fuel 18 b, a portion or all of partialoxidation gas 16 may be used in burner 1 as burner fuel 19.

The activated char produced in accordance with the invention exitscyclone 4 as stream 17 and is processed for its intended end use. Whenthe activated char is to be used to capture mercury in a flue gas streamfor example, stream 17 is entrained with a carrier gas (not shown) andinjected into the flue gas at a location where the temperature is withinthe desired range for mercury capture. The activated char is thencollected along with the fly ash in a particulate control device (PCD) 6(e.g., electrostatic precipitator or filter fabric) similar toconventional PAC injection for mercury control. As an alternative, theactivated char could be injected downstream of the PCD so that thecarbon content of the flyash does not destroy the ability to sell flyashas a component for cement. In other embodiments, activated char instream 17 is transported to its intended end use (e.g., a fixed bed forwaste water treatment).

The embodiment illustrated in FIG. 1 can be altered such that many ofthe process steps can be combined into the actual process equipment. Forexample and while not to be construed as limiting, a schematicrepresentation of a laboratory-scale system to produce activated char inaccordance with the present invention is shown in FIG. 2.

In this embodiment, burner 1 and reactor 3 are combined within theprocess equipment. Experience has shown that carbonaceous feedstock 13(coal in this example) ignites while still in mixing section 2 (notshown in FIG. 2), indicating ignition is extremely fast. Mixing section2 is attached to reactor vessel 3, which is a refractory lined pipe. Thedesign of the reactor 3 can be adjusted to account for proper residencetime within the reaction zone 3. Additive fluids or gasses 14, such aswater or steam, could be mixed anywhere in this embodiment, includingmixing upstream of the hot oxygen nozzle of burner 1 or into reactionvessel 3 (as shown in FIG. 2).

As further shown in FIG. 2, stream 9 may contain CO, H₂, CO₂ and N₂ (forexample, about 40% CO, 20% H₂, 20% CO₂ and 20% N₂ of the gases on a drybasis in stream 9) in addition to the char produced in the reaction zone3.

Nitrogen 15 is used to quench the products which are sent to cyclone 4.The use of nitrogen 15 as a quench media could be replaced with coolingtubes such that the composition of stream 9 is not altered.Alternatively, steam could be used as quench media 15. In this case, theconcentration of hydrogen and carbon dioxide entering the cyclone wouldbe altered from that in stream 9.

Cyclone 4 can be made from stainless steel. Combustible gasses can beflared using a natural gas-supported flame. Nitrogen 22 is used as aneductor gas to pump gases out of the cyclone. Gas 24 is thus heavilyconcentrated in nitrogen. Burner 26 shown in FIG. 2 is used for safetyprecautions in order to combust gases 24. As shown, the gases can be runthrough a natural gas-oxygen flare.

As further shown in FIG. 2, activated char 17 is collected from cyclone4 and can be further processed and used as discussed above withreference to FIG. 1.

FIG. 1 illustrates the use of hot partial oxidation gases 19 as fuel toburner 1 to replace some, if not all, of fuel 10 to heat oxidant 11.Another configuration of the present invention is shown in FIG. 3. Inthis exemplary embodiment, products 9 from reaction vessel 3 could beinjected directly into flue gas 20 for the removal of mercury from fluegas 20. It will be appreciated that stream 9 could be used for directinjection modes other than for the removal of mercury. As also shown inFIG. 3, stream 9 may be quenched using stream 15 as discussedhereinabove.

There is no combustion of the partial oxidation gases in the embodimentillustrated in FIG. 3. Accordingly, the activated char and partialoxidation gases formed in reactor 3 are injected together into flue gas20. In situations where no cyclone is used, the point of injection ofstream 9 (containing activated char and partial oxidation gases) islikely to be upstream in flue gas 20 relative to a configuration where acyclone is used. This is due to the additional time needed to allow thepartial oxidation gases to completely combust. The additional residencetime and temperature of the flue gas 20 allows the carbon monoxide toburn out (i.e. completely combust). More specifically, the temperatureof the flue gas at the point of injection in a configuration shown inFIG. 3 may be about 2000° F. as opposed to about 600° F. at the point ofinjection in FIG. 1.

EXAMPLE 1

Several samples of activated char were produced using the experimentalset-up illustrated in FIG. 2. Referring to FIG. 2, natural gas was usedfor stream 10, oxygen was used for stream 11 and Powder River Basin(PRB) coal was used for stream 13.

Listed in Table 1 are the stochiometric ratios (SR) used to make theactivated chars and the resulting properties of the chars. Forcomparison purposes, the properties of Darco® FGD, a powder activatedcarbon commercially available from Norit America, Inc., is also listedin Table 1.

SR_(HOB) was calculated by dividing the amount of oxygen required tocompletely combust the natural gas fed in stream 10 by the amount ofoxygen fed in stream 11. SR_(Reaction Vessel) was calculated by dividingthe amount of oxygen to completely combust the PRB coal fed in stream 13by the amount of oxygen entering reaction vessel 3.

The carbon content of the activated char was determined by using amuffle furnace to dry a sample of activated char and then to ignite thedried activated char sample. The carbon content was then calculated bydividing the difference between the initial mass and the final mass ofthe ignited sample by the initial mass of the dry activated char.

BET surface area of the activated char was measured using aMicrometrics® ASAP 2000 analyzer. It is noted that the BET surface areaof raw PRB coal is 5 m²/g.

The yield was calculated by using the carbon content of the activatedchar and by performing a material balance on the ash content of the PRBcoal fed in stream 13. The ash content of the PRB coal on a wet basis is4.47 %.

Mercury removals by the activated chars were evaluated using ElectricPower Research Institute's (EPRI's) Pollution Control System (PoCT) atWe Energies' Pleasant Prairie Power Plant, a 605 MW unit that burns PRBcoal. PoCT is a residence chamber used to simulate injection into thefirst field of a large scale ESP. During the mercury removal evaluation,a slipstream located upstream of Pleasant Prairie's cold side ESP wasextracted and then injected into the PoCT. Residence times of about 2and 4 seconds were tested and an activated char injection rate of about6 lb/MMacf was used. Percent mercury removal was calculated bysubtracting the outlet concentration of mercury from the inletconcentration of mercury and then dividing the sum by the inlet mercuryconcentration and multiplying by 100. Experiment number three was notevaluated for mercury removal. A more detailed description of themercury removal experimental set-up can be found in Sjostrom, et al.,“Assessing Sorbents for Mercury Control in Coal-Combustion Flue Gas”,Journal of the Air and Waste Management Association, Vol. 52, p. 902-911(August 2002). TABLE 1 Yield BET surface area Mercury Removal MercuryRemoval Experiment Number SR_(HOB) SR_(Reaction)Vessel Carbon Content %$\frac{lbchar}{lbcoal}\quad$ $\frac{m^{2}}{g}\quad$ 2 seconds residencetime % 4 seconds residence time % 1 6 0.7 58 0.11 237 41 44 2 6 0.3 820.25 225 22 24 3 3 0.3 81 0.24 361 ND ND Darco ®FGD NA NA 72 NA 474 4856

As shown in Table 1, as SR_(HOB) was decreased, while holdingSR_(Reaction Vessel) constant, the surface area increased. This isbelieved to be a result of the increased temperature and steam amount ofthe stream leaving section 1 of FIG. 2. Temperature, the amount ofoxidant and the exposure time of the char to the oxidant are importantfactors in determining the surface area. Generally, increasing any ofthe three factors increases the surface area.

Also, when SR_(Reaction Vessel) was increased, yield and carbon contentdecreased, surface area increased and mercury removal increased. It isbelieved that the yield and carbon content decreased because more oxygenwas supplied to the reaction vessel and as a result more carbon wasconsumed. It is also believed that the surface area increased as aresult of the explanation given above for increased surface due toincreased SR_(HOB).

If the invention is used to produce activated char at a central facilitysuch as a utility or cement kiln or a facility where the off-gas can beburned, the partial oxidation gases could be used in a boiler (or theburner) and the cooled activated char could be stored for use elsewhere.Alternatively or in addition, the activated char could be furtherprocessed (i.e. post-processed) to achieve specific desiredcharacteristics (e.g., steam treatments to increase surface area) ordoping of the activated char with a halide salt such as those disclosedin U.S. patent application Ser. No. ______, entitled “CatalyticAdsorbents For Mercury Removal From Flue Gas and Methods of ManufactureTherefor” to Chien-Chung Chao et al., referenced hereinabove.

In other embodiments of the invention, a hot gas stream other than hotoxygen can be created and used to activate the carbonaceous feedstockmaterial. For example, steam could be dramatically superheated by mixingthe steam with the products of a near stoichiometric oxy-fuel burner.This superheated steam would then be used to react with, and activatethe carbonaceous feedstock. It will also be appreciated by those skilledin the art that if it is desirable to solely pyrolyze (i.e., withoutcombustion), then other gasses such as nitrogen could also besuperheated in a similar fashion to pyrolyze the coal. In thisparticular embodiment, no residual oxygen would be present in stream 7(see figures above).

As discussed above, the present invention provides methods and systemsfor production of activated char that are sufficiently flexible andefficient such that production can occur near or at the end use site ofthe activated char. It will be appreciated, however, that production ofthe activated chars in accordance with the present invention is notlimited to onsite production. The methods and systems provided hereincan also be used in other arrangements. For example and while not to beconstrued as limiting, activated char produced by the present inventioncould be produced at a central facility and used to serve multipleutilities or the like. Another exemplary implementation could includeproducing activated char at a utility for that plant and shipping excessactivated char to other locations. It will also be appreciated that theactivated chars produced in accordance with the present invention can beused to replace PAC production used for other applications. The presentinvention thus provides versatility and flexibility with respect to thesite of production.

It should be appreciated by those skilled in the art that the specificembodiments disclosed above may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

1. A method for producing activated char, the method comprising:generating at least one gas stream containing an oxidant, the gas streamhaving a temperature of at least 800° F.; mixing carbonaceous feedstockwith the at least one gas stream such that the carbonaceous feedstockundergoes devolatilization and partial oxidation, thereby producingactivated char and byproducts.
 2. The method of claim 1, wherein thebyproducts comprise carbon monoxide and hydrogen.
 3. The method of claim2, wherein the byproducts are suitable for use as fuel.
 4. The method ofclaim 3, wherein the byproducts are used as a reburning fuel.
 5. Themethod of claim 1, wherein the activated char and the byproducts areproduced at a facility that utilizes the activated char.
 6. The methodof claim 1, further comprising quenching the powdered activated charwith a quenching media.
 7. The method of claim 6, wherein the quenchingmedia comprises a fog of water droplets.
 8. The method of claim 7,wherein the quenching media includes a dopant for doping the activatedchar.
 9. The method of claim 8, wherein the dopant is KBr.
 10. Themethod of claim 7, wherein the activated char is further treated withsteam to increase the surface area thereof.
 11. The method of claim 6,wherein the quenching media comprises nitrogen.
 12. The method of claim11, wherein the activated char is further treated with steam to increasethe surface area thereof.
 13. The method of claim 1, further comprisingadding a secondary reactive gas prior to mixing the carbonaceousfeedstock with the at least one gas stream.
 14. The method of claim 13,wherein the secondary reactive gas stream comprises steam.
 15. Themethod of claim 1, further comprising adding a solid, a liquid or agaseous additive subsequent to devolatilization and partial oxidation.16. The method of claim 1, wherein the temperature of the at least onegas stream is at least 2000° F.
 17. The method of claim 1, wherein theactivated char is a powder.
 18. The method of claim 1, wherein thecarbonaceous feedstock is selected from coals, petroleum coke, biomassmaterials, nutshells, nut hulls and mixtures thereof.
 19. The method ofclaim 18, wherein the carbonaceous material comprises coal.
 20. Themethod of claim 1, wherein the step of generating the at least one gasstream comprises mixing an oxidant and a fuel.
 21. The method of claim20, further including mixing steam with the oxidant and the fuel. 22.The method of claim 20, wherein the oxidant and the fuel are mixed at ornear the stochiometric ratio of the oxidant and the fuel.
 23. The methodof claim 20, wherein the oxidant and the fuel are mixed in a ratio ofexcess oxidant than the stochiometric ratio of the oxidant and the fuel.24. A method for producing activated char, the method comprising:generating a superheated gas stream, the gas stream having a temperatureof at least 800° F.; mixing carbonaceous feedstock with the superheatedgas stream such that the carbonaceous feedstock undergoesdevolatilization and partial oxidation, thereby producing activated charand byproducts.
 25. The method of claim 24, wherein the superheated gasstream comprises an inert gas and the carbonaceous feedstock undergoesdevolatilization and pyrolysis in substitution of devolatilization andpartial oxidation.
 26. The method of claim 25, wherein the inert gascomprises nitrogen.
 27. The method of claim 1, wherein the byproductscomprise carbon monoxide and hydrogen.
 28. The method of claim 24,wherein the byproducts are suitable for use as fuel.
 29. The method ofclaim 28, wherein the byproducts are used as a reburning fuel.
 30. Themethod of claim 24, wherein the activated char and the byproducts areproduced at a facility that utilizes the activated char.
 31. The methodof claim 24, further comprising quenching the powdered activated charwith a quenching media.
 32. The method of claim 31, wherein thequenching media comprises a fog of water droplets.
 33. The method ofclaim 32, wherein the quenching media includes a dopant for doping theactivated char.
 34. The method of claim 33, wherein the dopant is KBr.35. The method of claim 31, wherein the activated char is furthertreated with steam to increase the surface area thereof.
 36. The methodof claim 31, wherein the quenching media comprises nitrogen.
 37. Themethod of claim 36, wherein the activated char is further treated withsteam to increase the surface area thereof.
 38. The method of claim 24,further comprising adding a secondary reactive gas prior to mixing thecarbonaceous feedstock with the at least one gas stream.
 39. The methodof claim 38, wherein the secondary reactive gas stream comprises steam.40. The method of claim 24, further comprising adding a solid, a liquidor a gaseous additive subsequent to devolatilization and partialoxidation.
 41. The method of claim 24, wherein the temperature of the atleast one gas stream is at least 2000° F.
 42. The method of claim 24,wherein the activated char is a powder.
 43. The method of claim 24,wherein the carbonaceous feedstock is selected from coals, petroleumcoke, biomass materials, nutshells, nut hulls and mixtures thereof. 44.The method of claim 43, wherein the carbonaceous material comprisescoal.